asphalt developed specifically for COTA

May 2, 2012
asphalt developed specifically for COTA

At a glance the surface of the Circuit of The Americas racetrack will look just like that of a winding country road. But the engineering and testing that goes into the design and construction of a world class, Grade 1 motorsport track is far more high-tech, meticulous, custom-made and detailed than that for an average country road. 

With its vast experience in designing and overseeing the building of top-grade race tracks around the world, including the Circuit of The Americas in Austin, Texas, Tilke Engineers & Architects is working with Hart Consult International and local contractor and engineering companies to build the 20-turn 3.427-mile (5.516 km) track that will host the FORMULA 1 UNITED STATES GRAND PRIX™ Nov. 16-18.

“As the production limits are much tighter compared to national standard, we give special training to the construction companies, support and supervise design, production and paving,” said Dr. Rainer Hart. 

Dr. Hart is the managing director of Hart Consult International. Dr. Hart was involved in the construction of several test tracks and most of the F1 racetracks built since 1996. Working together with Tilke Engineers & Architects since 1985, he developed a special quality assurance system for race and test tracks which is used all over the world. 

The makeup of the asphalt was developed specifically for the Circuit of The Americas. 

“We don’t have any general racetrack mix design,” Dr. Hart explained. “A mix design has to be created for each track individually regarding climates, local standards, availability of suitable aggregates and bitumen. The quality of the aggregates is better compared to usual roads regarding resistance against polishing. The asphalt has special requirements and modifiers.” 

Asphalt is a mixture of bitumen, different sizes of aggregates and air. It is crucial that the coarse-textured surface of the track does not get polished smooth by the sliding tires of the F1 and other race cars, so a very high quality aggregate–made up of a mixture of sand, chippings and fillers–is used. Only preselected local quarries, which can provide superior products, are chosen as suppliers for track materials. This insures that the surface texture of the track remains “grippy” and provides optimum traction for the tires on the race cars.

The evenness and consistency of the track levelness overall, meanwhile, is practically as smooth and flat as a table. There will be no bumps, dips, uneven joint seams or variations on the track surface.

“The evenness will be much better (than the average road) because we will have four layers, laid by using a paver and special electronic leveling systems,” Dr. Hart said. “The evenness will be improved layer by layer.” 

The ultrasonic sensors insure that there no surface irregularity out of tolerance. It must meet the stringent required accuracy of +/- 0.315 of an inch (+/- 8mm). It is checked, lengthwise and crosswise to the paving direction on each lane, by using a 13-foot (4 meter) straight edge. 

Special care is paid to the tunnels and drain pipes running under the track because if the earthworks in these areas are not solid this could affect the uniformity of the track surface above.

Once that work is done and the foundation for the track–grading the soil, sand and gravel base–has been completed, work will focus on making sure there is no settlement of the earth below the track.  When that’s confirmed, the asphalt surface will be laid down.

The final composition of the layers, from top to bottom, is as follows:

  • 1.57 inches (4 cm) asphalt wearing course, modified for racing circuits;
  • 1.97 inches (5 cm) binder course;
  • 3.15 inches (8 cm) asphalt base course;
  • 17.72 inches (45 cm) crushed limestone road base/hydraulically bound base course; and
  • Two layers of crushed road base, upper layer laid by using a paver. 

Prior to this process, crews conduct test runs by laying asphalt in less critical areas. This insures that any problems or discrepancies can be revealed and resolved before the work begins on the actual track. This trial run was done in the paddock area, which is behind the pit garages, at the Circuit of The Americas. 

In this case, two pavers laid down two continuous lanes of tarmac, each 13.12-foot (4 meters) wide, without stops with one longitudinal joint. The pavement quality and asphalt density were checked with nuclear and non-nuclear density gauges. Core samples were cut out and extracted from the right, left and center joint for quality checks. 

Once work begins on laying the actual track surface, the pavers will run all day without stopping as stops might cause unevenness. The evenness will be checked continuously and other quality checks will also be made. 

The final result of all this intricate and high-tech design and construction will be a world-class racing experience at Circuit of The Americas that will be enjoyed by the fans and race drivers alike.

 

 

By Dan Knutson

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